[Ifeffit] Larch energy calibration

Matt Newville newville at cars.uchicago.edu
Wed Mar 3 18:38:24 CST 2021

Hi Valerie,

On Tue, Mar 2, 2021 at 10:48 AM Schoepfer, Valerie <
valerie.schoepfer at usask.ca> wrote:

> Hi,
> I am using Larch XAS Viewer for the first time to analyze some Mo XANES
> data. It is fairly straightforward, however I am running into problems with
> energy calibration, which leads to problems with Linear Combination
> Fitting.
> Right now, which is likely wrong, I’m calibrating the energy of a standard
> to the theoretical edge, then auto-aligning the samples to the standard.
> But how do reference foils fit in here? Reference foils don’t seem to be
> tied to the sample like they are in Athena. Should I be manually aligning?
> Is there a general guidance or work flow?

It's possible that I do not fully understand the question or that this
answer will veer a bit off the topic of your question.

For sure, energies need to be aligned properly for any multi-spectra
comparison or linear method to work well. But it should be that you will
have groups of spectra that all share a consistent energy calibration, say
from the same beamline/beamtime.

If you do have a reference channel for every measurement, you can compare
those reference channels.  Ideally, these will not vary for every
measurement - that would indicate a serious problem.   So, I think you
should be able to group spectra together as uniformly calibrated (hopefully
all data from a day or more of beamtime at a particular beamline) and then
make sure that the different groups of spectra.  Does that seem reasonable?

I have to admit that at my beamline I don't often have the luxury or need
to run a reference foil for every scan, so we calibrate consistently ahead
of time.  I'm sure that leads to a bias in the software.   I guess I forgot
that Athena had the ability to read and tie a second spectrum as a
"reference" and use that to auto-apply calibration.

Is it generally necessary to calibrate many spectra individually, or do
people find that doing them in a few large groups is sufficient?

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